Does Epistemic Non-Signalling Ensure the “Peaceful Coexistence” of Special Relativity and Quantum Nonlocality?

The standard notion of the fundamental indeterminism underlying quantum processes, including nonlocal entanglement phenomena as observed in EPR-type experiments, is thought to ensure the “peaceful coexistence” of relativity and nonlocality. By contrast, the development of an emergent quantum mechanics (EmQM) is chiefly concerned with theoretical approaches which have in common that they are deterministic in nature. The problem of determinism, which is attached to all so-called causal, local, or ontological theories that seek to account for quantum phenomenology including nonlocality, has been discussed extensively since the advent of the de Broglie-Bohm theory. In relation to dynamical nonlocality i.e. the observation of non-signalling correlations at space-like distances, how could deterministic theories not be in violation of special relativity?

In orthodox quantum mechanics, non-signalling correlations between space-like separated locations A and B are presumed to be ontic in nature. That is, non-signalling is not merely a function of the lack of empirical accessibility to any “hidden” signalling information between A and B. Critically, in orthodox theory no kind of signalling effect or signalling information is thought to exist whether or not that information is empirically accessible to any observer. By contrast, deterministic, ontological theories – at least those committed to free-measurement choice – must presume some kind of (superluminal) signalling influence across A and B. For that class of deterministic theories, the apparent violation of special relativity has often been addressed by their proponents using the following argument: Since the information associated with some signalling effect is empirically inaccessible, the information cannot be transmitted and communicated from A to B in a controlled, predictable fashion. Thus, the non-signalling principle remains unchallenged and the peaceful coexistence of relativity and nonlocality is thought to be ensured.

This presentation (1) provides an overview of key metaphysical assumptions which underlie popular approaches towards an EmQM and, against this background, (2) explores the validity of the above argument that epistemic rather than ontic non-signalling is sufficient to protect the integrity of the non-signalling principle. The metaphysics behind, and the reasoning for and against, the role of epistemic ignorance will be discussed in light of possible future research directions for an EmQM.